Accelerating Cosmologies from S-Branes

We point out that the recently proposed model of a flat 4-dimensional universe with accelerated expansion in string/M-theory is a special case of time-dependent solutions that the author found under the name of ``S-branes.'' We also show that similar accelerating models can be obtained from S-branes if the internal space is chosen to be hyperbolic or flat spaces.Comment: 8 pages, 4 figures, comments added, a typo corrected, final version to appear in Phys. Rev. Let

The Heterotic Dyonic Instanton

The static Yang-Mills-Higgs dyonic instanton is shown to have a non-vanishing, but anti-self-dual, angular momentum 2-form with skew eigenvalues equal to the electric charge; for large charge the angular momentum causes the instanton to expand into a hyper-spherical shell. A class of exact multi dyonic instantons is then found and then generalized to a new class of 1/4 supersymmetric, non-singular, stationary, exact solutions of the ten-dimensional supergravity/Yang-Mills theory. These self-gravitating dyonic instantons yield new heterotic string solitons, to leading order in the inverse string tension.Comment: 18 pages, LaTeX, no figures. Previous revision was to include exact multi-solitons. Third version corrects typos and ADM energy formul

Discovering the Sources of TFP Growth: Occupation Choice, Capital Heterogeneity, and Financial Deepening

The sources of "total factor productivity (TFP) growth" or the "Solow residual" typically remain unknown as a residual. This paper aims to identify the underlying sources of this residual growth, being explicit about micro underpinnings and transitional growth from occupation choices of heterogeneous agents and financial deepening in use of both macro and micro data. We develop a method of growth accounting that decomposes not only the overall growth but also the residual TFP growth into four components: occupational shifts, financial deepening, capital heterogeneity, and sectoral Solow residuals. Applying this method to Thailand, which experienced rapid growth with enormous structural changes for the two decades between 1976 and 1996, we find that 55 percent of TFP growth can be explained on average by occupational shifts and financial deepening, without presuming exogenous technical progress. Expansion of credit is a major part of this explained TFP growth. Decomposition of the simulation helps us to infer that for the remainder TFP growth, capital-heterogeneity effect is behind during the initial period (1976-1980) while sectoral Solow residuals, due to the surge of wage after 1986, is behind during the latter decade (1986-1996)TFP, Capital Heterogeneity, Occupation Choice, Financial Deepening

The credit risk-contingency system of an Asian development bank

This article offers a new method for the evaluation of financial institutions, one that combines socioeconomic survey data with appropriate accounting standards. A government-operated development bank in Thailand is found to be offering a risk-contingency or insurance system while being regulated as a more standard, loan-generating bank. Farmer clients experiencing adverse shocks receive indemnities that improve their well-being. With proper provisioning and accounts, that welfare gain could be weighed against premia or government subsidies.Financial crises - Asia ; Financial institutions - Thailand ; Thailand

Investigation of two-dimensional acoustic resonant modes in a particle separator

Within an acoustic standing wave particles experience acoustic radiation forces, a phenomenon which is exploited in particle or cell manipulation devices. When developing such devices, one-dimensional acoustic characteristics corresponding to the transducer(s) are typically of most importance and determine the primary radiation forces acting on the particles. However, radiation forces have also been observed to act in the lateral direction, perpendicular to the primary radiation force, forming striated patterns. These lateral forces are due to lateral variations in the acoustic field influenced by the geometry and materials used in the resonator. The ability to control them would present an advantage where their effect is either detrimental or beneficial to the particle manipulation process.The two-dimensional characteristics of an ultrasonic separator device have been modelled within a finite element analysis (FEA) package. The fluid chamber of the device, within which the standing wave is produced, has a width to height ratio of approximately 30:1 and it is across the height that a half-wavelength standing wave is produced to control particle movement. Two-dimensional modal analyses have calculated resonant frequencies which agree well with both the one-dimensional modelling of the device and experimentally measured frequencies. However, these two-dimensional analyses also reveal that these modes exhibit distinctive periodic variations in the acoustic pressure field across the width of the fluid chamber. Such variations lead to lateral radiation forces forming particle bands (striations) and are indicative of enclosure modes.The striation spacings predicted by the FEA simulations for several modes compare well with those measured experimentally for the ultrasonic particle separator device. It is also shown that device geometry and materials control enclosure modes and therefore the strength and characteristics of lateral radiation forces, suggesting the potential use of FEA in designing for the control of enclosure modes in similar particle manipulator devices

The optimal design of standard gearsets

A design procedure for sizing standard involute spur gearsets is presented. The procedure is applied to find the optimal design for two examples - an external gear mesh with a ratio of 5:1 and an internal gear mesh with a ratio of 5:1. In the procedure, the gear mesh is designed to minimize the center distance for a given gear ratio, pressure angle, pinion torque, and allowable tooth strengths. From the methodology presented, a design space may be formulated for either external gear contact or for internal contact. The design space includes kinematics considerations of involute interference, tip fouling, and contact ratio. Also included are design constraints based on bending fatigue in the pinion fillet and Hertzian contact pressure in the full load region and at the gear tip where scoring is possible. This design space is two dimensional, giving the gear mesh center distance as a function of diametral pitch and the number of pinion teeth. The constraint equations were identified for kinematic interference, fillet bending fatigue, pitting fatigue, and scoring pressure, which define the optimal design space for a given gear design. The locus of equal size optimum designs was identified as the straight line through the origin which has the least slope in the design region